In clutches for automotive vehicles and the like, it is common to use a clutch disc assembly comprising a drive member in the form of a disc and a driven member with circumferentially spaced springs interposed in aligned openings in the disc and driven member that are operable to function in stages. The springs forming the first stage function to reduce vibration and noise in the neutral or non-driving position and the springs of the second stage function to provide the drive as the clutch is engaged. In order to further reduce the noise, it has been common to provide friction means between the driving disc and driven member. Hysteresis is a name given to the frictional torque in a clutch disc damper. Reducing or eliminating neutral rollover noise in some vehicles requires a first stage with low spring rates and low hysteresis levels. However, best performance in the load carrying second stage may require a relatively high hysteresis. Very often the range of hysteresis which provides the best neutral performance does not overlap the hysteresis range which gives the best performance in a driving condition. In a case such as this, a damper with the same hysteresis level in each stage may not provide acceptable performance under both conditions. A device which allows the hysteresis to be tuned to a higher level in the second stage than the first is therefore desirable.
Inasmuch as the requirements for idling differ substantially from those in the driving position, the friction preferably should be at a low level in the first stage and isolated from the friction in the second stage such that the frictional torque or hysteresis is less in the first stage than in the second stage in order to provide the best performance.
Accordingly, among the objects of the present invention are to provide a clutch disc assembly wherein the friction of the first stage is independent of the second stage and wherein the friction of the second stage can be changed without affecting the friction of the first stage.